Re: [PATCH 8/8] btrfs: remove BTRFS_INODE_READDIO_NEED_LOCK

[Nikolay Borisov <nborisov@suse.com>]

On 11.12.19 г. 1:01 ч., Goldwyn Rodrigues wrote:
> From: Goldwyn Rodrigues <rgoldwyn@suse.com>
> 
> Since we now perform direct reads using i_rwsem, we can remove this
> inode flag used to co-ordinate unlocked reads.
> 
> The truncate call chain gets the i_rwsem which may conflict with direct

nit: Truncating taking i_rwsem means it's correctly synchronized with
concurrent DIO reads. So it's protected, just the wording needs to be
tweaked.

> reads:
> do_truncate <-- calls inode_lock
>   notify_change
>    ->setattr/btrfs_setattr
>      btrfs_setsize
> 
> Signed-off-by: Goldwyn Rodrigues <rgoldwyn@suse.com>
> Reviewed-by: Nikolay Borisov <nborisov@suse.com>
> ---
>  fs/btrfs/btrfs_inode.h | 18 ------------------
>  fs/btrfs/inode.c       |  5 -----
>  2 files changed, 23 deletions(-)
> 
> diff --git a/fs/btrfs/btrfs_inode.h b/fs/btrfs/btrfs_inode.h
> index 4e12a477d32e..cd8f378ed8e7 100644
> --- a/fs/btrfs/btrfs_inode.h
> +++ b/fs/btrfs/btrfs_inode.h
> @@ -27,7 +27,6 @@ enum {
>  	BTRFS_INODE_NEEDS_FULL_SYNC,
>  	BTRFS_INODE_COPY_EVERYTHING,
>  	BTRFS_INODE_IN_DELALLOC_LIST,
> -	BTRFS_INODE_READDIO_NEED_LOCK,
>  	BTRFS_INODE_HAS_PROPS,
>  	BTRFS_INODE_SNAPSHOT_FLUSH,
>  };
> @@ -317,23 +316,6 @@ struct btrfs_dio_private {
>  			blk_status_t);
>  };
>  
> -/*
> - * Disable DIO read nolock optimization, so new dio readers will be forced
> - * to grab i_mutex. It is used to avoid the endless truncate due to
> - * nonlocked dio read.
> - */
> -static inline void btrfs_inode_block_unlocked_dio(struct btrfs_inode *inode)
> -{
> -	set_bit(BTRFS_INODE_READDIO_NEED_LOCK, &inode->runtime_flags);
> -	smp_mb();
> -}
> -
> -static inline void btrfs_inode_resume_unlocked_dio(struct btrfs_inode *inode)
> -{
> -	smp_mb__before_atomic();
> -	clear_bit(BTRFS_INODE_READDIO_NEED_LOCK, &inode->runtime_flags);
> -}
> -
>  /* Array of bytes with variable length, hexadecimal format 0x1234 */
>  #define CSUM_FMT				"0x%*phN"
>  #define CSUM_FMT_VALUE(size, bytes)		size, bytes
> diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
> index ce53f2889673..4c76a6d5e6a4 100644
> --- a/fs/btrfs/inode.c
> +++ b/fs/btrfs/inode.c
> @@ -5273,11 +5273,6 @@ static int btrfs_setsize(struct inode *inode, struct iattr *attr)
>  
>  		truncate_setsize(inode, newsize);
>  
> -		/* Disable nonlocked read DIO to avoid the endless truncate */
> -		btrfs_inode_block_unlocked_dio(BTRFS_I(inode));
> -		inode_dio_wait(inode);
> -		btrfs_inode_resume_unlocked_dio(BTRFS_I(inode));
> -
>  		ret = btrfs_truncate(inode, newsize == oldsize);
>  		if (ret && inode->i_nlink) {
>  			int err;
>